The Growth of Galaxies: Ways Forward toward a More Robust Understanding at High Redshift

The Growth of Galaxies:Ways Forward toward a More Robust

Understanding at High Redshift

Mark Dickinson (NOAO)

3 November 2006 Mark Dickinson - MGCT2

GOODS: Great Observatories Origins Deep Survey

The demographics of galaxy growth

• Star formation• Stellar mass• Galaxy merging



Cosmic star formation: a plethora of measurements…

Hopkins & Beacom 2006



The global history of cosmic star formation

• The “cosmic” SFR(z): the comoving average SFR from galaxies, per unit volume, over cosmic time and redshift.

• What does it relate to?– Growth of stellar mass in galaxies ((M*) vs. z)– Depletion of gas ((HI) vs. z)– Build-up of metals ((Z) vs. z)– Supernova rates vs. z– Ionizing background radiation– Extragalactic background light



Introduction, cont’d

• The era of multiwavelength measurements– UV– Mid-IR– Far-IR– Submm – Radio– Nebular emission lines– X-ray

• General challenges:– No one observable sees it all– Interpreting observables: model dependence– The IMF– Stellar population/evolution issues



SFR(z) vs. *(z): tension at all redshifts?

SFR(z) stars(z)

Derived SFR(z) may overproduce derived W*(z) at most redshifts

Hopkins & Beacom 2006; see also Chary & Elbaz 2001; Dickinson et al. 2003; Ferguson et al. 2003



Stellar mass density, z~5 to 6

Stark et al.

Eyles et al.

Wiklind et al.

*(reion.),

6 < z < 10,C=30, fesc=1

Stars whose formation produces sufficient reionizing photons at 6<z<10 for 100% Lyman contin. escape fraction (Madau, Haardt & Rees 1999)

Estimates for * at z=5-6 are 5-50x smaller than at z~2-3

Yan et al. 2006



SFR demographics:GALEX UV at z < 1.2

Schiminovich et al. 2005

Arnouts et al. 2005

HDF N+S,Steidel’99

GALEX



Deep ISO surveys

Chary & Elbaz 2001: Modeled deep number counts from ISO 15, 90, 170m, SCUBA 850m surveys, and the CIRB

Minimal redshift information; small statistics

Features:• LIRGs dominate SFR at z~1• Fairly flat SFR(z) from 0.8 < z < 2; Turnover pushed toward lower z.



Into the Spitzer era

Vastly improved statisticsDeeper dataRedshifts!

Le Floc’h et al. 2005



Evolution of the IR luminosity density, 0 < z

< 1

0 < z < 1:UV(z) ~ (1+z)2.5

(Schiminovich et al. 2005)IR(z) ~ (1+z)3.9

(Le Floc’h et al. 2005)

Infrared/UV emitted energy from star formation:

z=0 ~1.5 : 1z=1 ~ 4 : 1

LIRGs

ULIRGs

Normal Galaxies

Total IR

- - - UV - - -

Le Floc’h et al. 2005



Challenges: going deep enough

24m-derived IR LFs, z < 1.2: Le Floc’h et al. 2004Spitzer wide surveys reach LIR ~ 1011 Lo at z~1, ~ 1012 Lo at z~2.

Potentially large and uncertain LF extrapolation to total energy density:

Have we really converged on (SFR) at z ~ 1 ?

Deep surveys (GOODS) cover small area and volume (cosmic variance).



GOODS MIPS 24 m

~2000 24m sources with spectroscopic z

GOODS MIPS data detects dust + PAH emission from LIRGs at z ~ 2-3



GOODS MIPS 24 m

At 1 < z < 2.5, MIPS 24m is ~10 to 1000x more sensitive to star formation than are deep VLA or SCUBA surveys.



z ~ 2-3: the ULIRG era?

Chary et al. - Work in progress!

Caveats:

• Spectroscopic (and photo-?) z samples incomplete)

• Templates for MIR-to-SFR conversion uncertain, esp. at higher L and higher z

• AGN identification uncertain

• SF component of AGN IR emission uncertain



Ways forward: SF demographics

Forthcoming:– Deeper MIPS surveys over wider areas: Far-IR Legacy Survey; S-COSMOS

• Deeper at 24 m: hopefully below the LF knee at z~1; possibly convergence at z~2

• Multiple fields: controlling cosmic variance

Desperately needed:– Redshifts!! Especially for dusty galaxies/AGN at z > 1.

• Mid-IR K-corrections potentially very strong with small z.• Many of the galaxies which may dominate (SFR) at z~2:

– are not UV bright– have K > 20

• Multiplexed NIR spectroscopy and wild heroism? Let’s hope so…

Open issues:– AGN contribution to IR emission– Star formation contribution from those AGN– Mid-IR to SFR conversions



Challenges: MIR/SFR calibrationrest frame 12 m at z ~ 1

z ~ 0 IRAS BGS12 mL12 ~ LIR

0.91

0.8 < z < 1.2 GOODS 24m vs. 1.4 GHz

20 cm fluxes -> LIR assuming z~0 radio/FIR correlation (Yun et al. 2001)MIPS 24m -> L(12m) with minimal k-correctionSignificant number of radio-loud outliers at z~1 (e.g., Donley et al. 2005)

L1.4GHz > 1023 WHz-1 : 38% outliers(>7% of z~1 sources with f(24m) > 20Jy)

z=0

rela

tion



PAH emission and SF

SWIRE+SDSS: Tight 8m / 70m correlation, but with strong Z dependence

12+log(O/H) > 8.8:L8 ~ LIR

0.9, < 0.126 dex

Lower O/H -> low L8/L70

Trend starts just below Zsolar

Monekiewicz et al. 2006



Challenges: calibrating 24m/SFR at z~2

MIPS: <f(24m)>=125 Jy, <z>=1.9, and CE01 templates: <LIR> = 1.7e12 Lo, <SFR> ~ 300 Mo/yr

UV continuum + reddening: <SFR> ~ 220 Mo/yr

Radio: stacked VLA data <f(20cm)> = 17 Jy<LIR> = 2e12 Lo, <SFR> ~ 340 Mo/yr

Sub-mm: stacked <f(850m)> = 1.0 mJy (5) <LIR> = 1.0e12 Lo, <SFR> ~ 170 Mo/yr

X-ray: stacked 8.5 soft-band detection, no significant hard-band. Far below expected AGN level. <SFR> = 100 - 500 Mo/yr (Ranalli 2003, Persic 2004 conversions)

On average, multiwavelength SFR tracers agree reasonably wellwith expectations from low-z correlations, templates & analogs.

Daddi et al. 2005



Object by object SF comparisons at z~2

Daddi et al. in prep.Reddy et al. in prep.

24 m vs. H

24 m vs. radio



Submm emission, dust temperatures, etc.

“warm” CE01“cool” CE01 (+ extra mid-IR extinction)

850mm too bright relative to radio or 24mm when comparedWith “warm” local ULIRG templates appropriate for these large L(IR).

Pope et al. 2006



Implied dust temperatures

Chapman et al. 2005850m/20cm flux ratios suggest cooler dust temperatures for the implied FIR luminosities, compared to the local LIR-T correlation.



Ways forward: SF calibration

• Measure true thermal far-IR dust emission: luminosities and temperatures– Deeper, wider Spitzer 70 m surveys– Herschel (70-500 m)– SHARC2, SCUBA2, etc. (e.g. 350-450 m)– ALMA

• Improved cross-calibration & diagnostic checks of SF:– Mid-IR vs. far-IR, submm, radio– Extensive mid-IR spectroscopy - Spitzer IRS

MIPS 24 mM81 = NGC 3031 24 m

H + RM81 = NGC 3031 H+ R



24 m rest frame emission traces star

formation

Calzetti et al. 2005M51

Calzetti et al. in prep.



600s GTO exposure

Ultradeep 70m imagingFrayer et al. 2006 + new MIPS Legacy Survey

10800s GO exposure, ~10’x10’



Spitzer Far-IR Legacy Survey

GOODS-S

E-CDFS: 30’x30’EGS/AEGIS: 90’x10’

~2000 arcmin2 total

10x current GOODS 70m6.5x deep GOODS 24m

Sensitivities: ~3 mJy @ 70m~30 Jy @ 24m

LIR ~ 1011.5Lo at z=1LIR ~ 1012.5Lo at z=2

+160 arcmin2 in GOODS-N





Deep 70 m matched to radio and submm

450m

70m70m survey limit well matched to very deep SCUBA-2 450m surveys and to very deep 20cm VLA surveys:

• LIRGs at z~1• ULIRGs at z~2

24m survey will reach “near-GOODS” depth over much larger areas:

• Normal galaxies at z~1• LIRGs at z~2



70m constrains dust properties at high redshift

70m/24m: warm dust properties450m/70m: bulk dust temperatures

SCUBA-2!Dusty AGN



SFR(z): the first 2 Gyr

• At z > 3, UV is (almost) the only game in town: no direct measurement of reprocessed energy for most galaxies (yet).– Spitzer, Herschel, and near-term submm facilities can only

detect hyperluminous (unlensed) objects

– ALMA: LIR = 1011 Lo at z=6 in ~10 hours

– JWST: H at z < 6.5

• Difficulties:– Uncertain extinction inferred from UV spectral slope alone.– Apparently very steep (but uncertain) UV LF slopes

-> very large corrections to total luminosity density



Mass from light



Stellar mass:stellar population issues

The IMF:• The IMF almost certainly flattens/turns over at low mass.

We use Salpeter because we’re lazy.• Low-mass turnover is probably not a big problem:

– It affects M*/L more or less uniformly at all wavelengths, including both stellar mass and SFR indicators.

– Local evidence points to nearly universal low-mass IMF• IMF slope at intermediate/high mass is a big deal!

– Affects different SFR indicators differently– Changes luminosity evolution of stellar populationsFortunately, so far there’s not much convincing evidence for

IMF slope variations.



SFR(z) vs. *(z): tension at all redshifts?

SFR(z) stars(z)

Derived SFR(z) may overproduce derived W*(z) at most redshifts

Hopkins & Beacom 2006; see also Chary & Elbaz 2001; Dickinson et al. 2003; Ferguson et al. 2003



Stellar population issues (2)

Star formation histories:• Broad band SEDs are largely degenerate to a variety of

possible past SF histories, which can lead to substantial M/L variations.

• Modeling often assume smooth, monotonic SF histories, but recent SF can mask hide high-M/L starlight from older stars.

• IRAC improves but does not eliminate this, especially for bluer, star-forming galaxies.



Mass from light



Composite stellar populations

Significant mass from an older stellar population could be hidden by ongoing star formation.

Papovich et al. 2001















IRAC observations of galaxies at z ~ 4-5

z~4 B-dropouts z~5 V-dropouts



Stellar population issues (3)

The models:• No definite convergence on stellar population synthesis

models yet.• In particular, Maraston 2006 models:

– Larger red light contribution from TP-AGB stars at 0.2-2 Gyr– Different evolutionary tracks– Warmer RGB temperaturesRedder colors and lower red/near-IR M/L at t < 2 GyrBluer colors at later times

This reduces derived stellar pop. masses and ages at high redshift



Stellar population models

Stellar mass may also be reduced by changing stellar population models:

• Maraston 2005 models with substantial TP-AGB contribution to red/near-IR light at ages of 0.2-2 Gyr can reduce M/L significantly



Testing stellar M/L at high z

• Almost only SED modeling: at high redshift, almost no direct tests of stellar masses so far!– Galaxy kinematics to constrain M/L (mostly FP for

early-type galaxies; see also RvdM talk)– Issues of dark matter effects in observed large-scale

internal kinematics

• AO-fed integral field spectroscopy may be the best way forward.



Galaxy merging

Galaxies grow their mass both by star formation and merging.A full understanding of galaxy growth requires understanding

both.

• Stellar mass (M*) + star formation (dM*/dt)SF distribution functions versus time (t, z) are in principle sufficient …

• … but in practice real measurements of merger rates (ideally versus other galaxy properties (M*, SFR) would help a lot!!

• Observationally, still a highly debated topic, even at z < 1• In lieu of definitive data, models must guide us here.



The near-infrared data gap

• Near-IR data remain a huge bottleneck:– Much shallower than current deep optical or Spitzer/IRAC

imaging.– Photo-z’s remain mandatory (unfortunately) and near-IR is

the weakest link.• Wide-field IR ground-based imagers:

– WFCAM, WIRCAM, NEWFIRM, VISTA, HAWK-I, MOIRCS, FLAMINGOS-2, etc.

• HST/WFC3:– Detect fading red remnants of higher-z star formation– Differentiating stellar population components within galaxies– Measure UV spectral slopes (dust reddening) at z > 5– Photometry/SEDs/photo-z’s for UV-faint galaxies at z > 5– Reliable 2-color LBG selection at 6 < z < 10+





Stellar mass density, z~5 to 6

Stark et al.

Eyles et al.

Wiklind et al.

*(reion.),

6 < z < 10,C=30, fesc=1

Stars whose formation produces sufficient reionizing photons at 6<z<10 for 100% Lyman contin. escape fraction (Madau, Haardt & Rees 1999)

Estimates for * at z=5-6 are 5-50x smaller than at z~2-3

Yan et al. 2006



Ways Forward: a summary

• Fully exploit existing surveys: the era of “precision L(z)”• More redshifts! (and more reliable redshifts!)• Extend multi- correlation studies at all redshifts

– MIR, FIR, radio, UV, X-ray, H, etc.– Deeper radio and FIR vital: SCUBA-2, Herschel, ALMA…

• Mid-IR improvements:– Better mid-IR spectral templates– IRS spectral diagnostics for large high-z samples– Figure out the physics!!! (esp. MIR, PAHs, etc.)

• Measure dust temperatures at high z• Get stellar evolution straight (stellar pop. models)• It’s the IMF, dummy (esp. at intermediate & high masses)• Better measurements of merger rates (vs. z & other properties)• Insanely deep surveys at z~5-6 and beyond (WFC3; JWST; ALMA;

TMT)



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The Growth of Galaxies: Ways Forward toward a More Robust Understanding at High Redshift

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